'Darker-than-black' metamaterial could lead to more efficient solar cells

When a hyperbolic metamaterial is corrugated, its reflectance is greatly reduced and it becomes "darker than black." Image credit: E. E. Narimanov, et al.

(PhysOrg.com) -- If typical black paint absorbs about 85% of incoming light, then a newly designed metamaterial that absorbs up to 99% of incoming light may be considered darker than black." By taking advantage of the unique light-scattering properties of metamaterials, researchers have discovered that a hyperbolic metamaterial with a corrugated surface can have a very low reflectance, which could make it promising for high-efficiency solar cells, photodetectors, and radar stealth technology.

The researchers, E. Narimanov, et al., from Purdue University and Norfolk State University, have posted their study on the radiation-absorbing metamaterial at arXiv.org.

In their study, the researchers fabricated a hyperbolic metamaterial out of arrays of silver nanowires grown in alumina membranes. They found that this material absorbed about 80% of incoming light. Then, they ground the surface of the metamaterial to produce corrugations and defects, which they predicted would dramatically reduce the light reflection, increasing the absorption. Their measurements showed that the corrugated metamaterial absorbed up to 99% of incoming light, and that the radiation-absorbing capability is applicable to all parts of the electromagnetic spectrum.

As the scientists explained, the metamaterials very low reflectivity results from one of its hyperbolic properties: an infinite density of photonic states. This super singularity greatly increases the amount of light scattering from surface defects and corrugations in the metamaterial. The defects and corrugations scatter light primarily inside the material, basically sucking photons inside the hyperbolic medium.

The researchers predict that the new metamaterial will provide a new route toward designing radiation-absorbing materials. As light absorption plays a key role in solar cells and many other applications, the researchers plan to investigate these possibilities in the near future.

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16 comments

The wings of Morpho moths don't contain any metal, although they're quite reflective. We should realize, this effect is based on interference of light and a such it can be easily reversed. Many black wings of moths and birds could be actually caused not with black pigments, but with photonic "superabsorbers".

In the 70's I built my first telescope. I made the center tube out of foam which I hollowed out. It left "nooks and crannies" in the foam sidewall which I though would be great for capturing light. I painted it flat black and sure enough it was one of the best deep field scopes I ever built. Give anyone any ideas?

- Silver nanowires grown in alumina membranes. Sounds like once it gets dirty, it'll never be clean again. So, not for stealth.

- Just the fact that some material seems black, doesn't automatically mean it's good for solar arrays. These are two separate things. (I know this is hard to get for most science editors.) Yes, a very efficient solar panel would appear dark. But if I mix a blacker paint than the neighbor, that blackness doesn't imply my paint is any better than his for making electricity.

- Increasingly, we find articles written by people who have not even skimmed previous issues of the same publication. Trivial news are repeatedly presented as leading edge stuff.

- The author does not bother to even mention what the word Hyperbolic means in this context. (But yes, any time there is a cosmology article, the writer painstakingly explains that a light-year is the distance a ray of light covers in a year. Sigh.)

way back there was a researcher who created a 'darker than black' absorbing surface by exposing it to a femtosecond laser of extremely high energy state. the mere exposure of the surface to such a high and powerfullyfocussed beam of energy , albeit for only a femto second, was enough to change it to a surface far more absorbing than ordinary black surfaces.

i wonder if the mechanism of action upon the surface produced the same surface geometry to cause the high absorbtion as was observed in this article.

The article is just cluttering up the internet with a misleading title. When you start to read you realize they mean "blacker than before" or "less reflective than has been achieved". Darker than black is not what is achieved here. At best you could say "darker than paints that are typically labeled black".

Increasingly, we find articles written by people who have not even skimmed previous issues of the same publication. Trivial news are repeatedly presented as leading edge stuff

It's not only problem of superficial journalism. IMO it's the consequence of over-employment in science, which forces the scientists to intentionally produce higher number of articles with lower value added. They often publishing the redundant research, just under different name. The journalists are getting disoriented with increasing number of article topics easily, after then...

For example, I consider the gravitational waves, CMBR noise, fat strings and gravitons as the same experimental manifestation of extradimensions of space-time. Nevertheless, they're all still named and searched independently - which enables the physicists to earn more money with studying of the same phenomena.

It goes beyond black... I think completely non-reflective would appear as if it were a rip in the universe or a defect in your vision or something, at least if you didn't already know what you were looking at.

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